A circuit breaker of the type just mentioned was described in Assignee's French patent application No. 82 00034, dated Jan. 5, 1982. In that design, said gas volume is annular and bounded by the inside wall of a gas blast nozzle and by a baffle or deflector coaxial with the nozzle.
The above-mentioned circuit breaker is illustrated in partial half-cross-section in FIG. 1, the various reference numbers therein designating the following items:
1: Main fixed contact (1--in open position; 1'--in closed position) PA0 2: Fixed arcing contact PA0 3: Main moving contact PA0 4: Insulating gas blast nozzle PA0 5: Coaxial deflector PA0 6: Openings between volumes 9 and 13 PA0 7: Fingers of main moving contacts PA0 8: Tubular portion of moving contact; 8A--end of contact tubular portion PA0 9: Annular cross-section volume for thermal effect PA0 9A: Annular volume adjacent to volume 9 PA0 10A: Annular passage for hot gas providing arc blasting by thermal effect PA0 10B: Annular passage for gas from compressed gas blast nozzle PA0 12: Fixed puffer piston PA0 13: Compression volume PA0 14: Annular blasting duct.
It can be seen that, on opening of the breaker, the arc which forms between the fixed arc contact 2 and contact 8A is blasted with gas coming from volumes 9 and 13. Volume 9 contains gas which is compressed as a result of heating by the arc and is therefore called the thermal volume; volume 13 carries air moved by the piston 12 and accordingly is called the compression volume.
It is apparent that the arc is powerfully blasted only in the area near its roots which spring from the moving contact 8A. Thus, to obtain efficient quenching of arcing from large currents, requires a considerable jet of gas from the compression volume and duct 13, 14. Yet the greater the gas blast, the greater the energy required to deliver the blast, which must overcome the back-pressure on the piston 12.
It is the object of this invention to improve the blasting effect without increasing the actuating energy.
It has been proposed to improve blasting efficiency by arranging the thermal and compression volumes to each side of the arcing region.
Such an approach is described in German patent applications Nos. 1 127 442 and 29 48 976 and in French Pat. No. 2 373 141.
However, in the circuit breakers described in the foregoing documents, the gases coming from the two volumes are brought together prior to reaching the arcing region, with the result that only a small improvement in blasting or blow-out efficiency is provided.
One of the features of the present invention is that the gases coming from the thermal and the compression volumes are routed through nozzles which direct separate blasts to each of the arc roots respectively.